Seasonal variation of phytoplankton and productivity in the surf zone and backwater at Cochin

Abstract

Seasonal variation of phytoplankton abundance and productivity were studied in the surf zone of the sea at Cochin and the Cochin backwater with reference to cell counts, chlorophyll and photosynthesis in relation to hydrographic parameters for a period of two years (Janu- ary 2001 to December 2002). Phytoplankton density and diversity indicated a decline as com- pared to the earlier studies. In the surf zone, diatoms contributed about 99% of phytoplank- ton cells. Seasonal cycles observed in the current and earlier studies indicated that there is no egular seasonal trend in the distribution and abundance of phytoplankton in the nearshore waters. The cell counts and productivity values showed wide fluctuation within the seasons and from season to season. In the surf zone, chlorophyll n content and photosynthetic productivity recorded higher values during southwest monsoon season and in the backwater during postmonsoon period. The study revealed that the surf zone was relatively more productive in terms of cell density and species diversity as compared to the Cochin backwater. Factors influencing fluctuation and abundance of phytoplankton in the nearshore waters are briefly discussed.